Light emitting diode chip having distributed bragg reflector and method of fabricating the same

ABSTRACT

A light-emitting diode chip configured to emit light of a first wavelength range and light of a second wavelength range, including a substrate, a light-emitting structure disposed on a first surface of the substrate, the light-emitting structure including an active layer disposed between a first conductivity-type semiconductor layer and a second conductivity-type semiconductor layer, and configured to emit light of the first wavelength range, and first and second distributed Bragg reflectors (DBRs) disposed on a second surface of the substrate. The first DBR is disposed closer to the substrate than the second DBR, the first wavelength range comprises a blue wavelength range, the first DBR comprises a higher reflectivity for light of the second wavelength range than for light of the first wavelength range, and the second DBR comprises a higher reflectivity for light of the first wavelength range than for light of the second wavelength range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/023,876, filed on Feb. 9, 2011, now issued as U.S. Pat. No.8,963,178, which is a continuation-in-part of U.S. application Ser. No.12/917,937, filed on Nov. 2, 2010, now issued as U.S. Pat. No.8,907,360, and claims priority from and the benefit of Korean PatentApplication No. 10-2010-0013166, filed on Feb. 12, 2010, Korean PatentApplication No. 10-2010-0115347, filed on Nov. 19, 2010, and KoreanPatent Application No. 10-2009-0109870, filed on Nov. 13, 2009, whichare hereby incorporated by reference for all purposes as if fully setforth herein.

BACKGROUND

1. Field

Exemplary embodiments of the present invention relate to a lightemitting diode chip and a method of fabricating the same, and to a lightemitting diode chip having a distributed Bragg reflector and a method offabricating the same.

2. Discussion of the Background

A gallium nitride-based light emitting diode chip emitting blue orultraviolet wavelength light may be used for various applications. Inparticular, various types of light emitting diode packages emittingmixed color light, for example, white light required for a backlightunit, general lighting, or the like, have been marketed.

Since the light output from the light emitting diode package may dependon the light emission efficiency of the light emitting diode chip,research to improve the light emission efficiency of the light emittingdiode chip has been continuously conducted. In particular, attempts toimprove the light extraction efficiency of the light emitting diode chiphave been performed. For example, technology of forming a metalreflector or a distributed Bragg reflector (DBR) on a bottom surface ofa transparent substrate such as a sapphire substrate has beenresearched.

FIG. 1 shows reflectivity measured by forming an aluminum layer on thebottom surface of a sapphire substrate according to the related art.

It can be appreciated from FIG. 1 that in the case of the sapphiresubstrate on which the aluminum layer is not formed, reflectivity ofabout 20% is shown, but in the case of the sapphire substrate on whichthe aluminum layer is formed, reflectivity of about 80% is shown over avisible wavelength range.

FIG. 2 shows the reflectivity measured by the DBR formed by periodicallyapplying TiO₂/SiO₂ to the bottom surface of the sapphire substrateaccording to the related art.

As shown in FIG. 2, when the DBR is formed to reflect light emitted fromthe light emitting diode chip, for example, emitted light having a peakwavelength of 460 nm. FIG. 2 shows that reflectivity in the lightemitting diode using the DBR may reach approximately 100% in a bluewavelength range, for example, a wavelength range of 400 to 500 nm.

However, the DBR can only increase the reflectivity for a part of thevisible range. Therefore, the reflectivity for other ranges isconsiderably lower than that shown in FIG. 2 for the wavelength range of400 nm to 500 nm. That is, as shown in FIG. 2, the reflectivity for awavelength of about 520 nm or more is suddenly reduced while most of thereflectivity is less than 50% at a wavelength of 550 nm or more.

Therefore, when mounting the light emitting diode chip using the DBR ina light emitting diode package to emit white light, the DBR shows highreflectivity for light of the blue wavelength range emitted from thelight emitting diode chip but the DBR does not show efficient reflectioncharacteristics for light emitted in the green and/or red wavelengthranges. Therefore, there is a limit in improving the light emissionefficiency of the light emitting diode package.

SUMMARY

Exemplary embodiments of the present invention provide a light emittingdiode chip capable of increasing light emission efficiency of a lightemitting diode package implementing a mixed color light, for example,white light, and a method of fabricating the same.

Exemplary embodiments of the present invention also provide a DBR havinghigh reflectivity over a wide wavelength range and a light emittingdiode chip having the same.

Additional features of the present invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the present invention.

An exemplary embodiment of the present invention discloses a lightemitting diode chip including a substrate having a first surface and asecond surface, a light emitting structure arranged on the first surfaceof the substrate, the light emitting structure including an active layerarranged between a first conductive-type semiconductor layer and asecond conductive-type semiconductor layer, a distributed Braggreflector arranged on the second surface of the substrate, thedistributed Bragg reflector to reflect light emitted from the lightemitting structure, and a metal layer arranged on the distributed Braggreflector. The distributed Bragg reflector has a reflectivity of atleast 90% for light of a first wavelength in a blue wavelength range,light of a second wavelength in a green wavelength range, and light of athird wavelength in a red wavelength range.

An exemplary embodiment of the present invention also discloses a methodof fabricating a light emitting diode chip, the method including forminga light emitting structure on a first surface of the substrate, removinga portion of the substrate by grinding a second surface of thesubstrate, and after the grinding, reducing the surface roughness of thesecond surface of the substrate by lapping the substrate, and forming adistributed Bragg reflector on the second surface of the substrate. Thelight emitting structure includes a first conductive-type semiconductorlayer, a second conductive-type semiconductor layer, and an active layerdisposed between the first conductive-type semiconductor layer and thesecond conductive-type semiconductor layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification, illustrate exemplaryembodiments of the present invention, and together with the descriptionserve to explain the principles of the present invention.

FIG. 1 is a graph showing reflectivity of aluminum on a sapphiresubstrate according to the related art.

FIG. 2 is a graph showing reflectivity of a distributed Bragg reflectoron the sapphire substrate according to the related art.

FIG. 3 is a cross-sectional view showing a light emitting diode chiphaving the distributed Bragg reflector according to an exemplaryembodiment of the present invention.

FIG. 4 is a magnified cross-sectional view of the distributed Braggreflector of FIG. 3.

FIG. 5 is a cross-sectional view showing a distributed Bragg reflectoraccording to another exemplary embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a light emitting diode chiphaving a plurality of light emitting cells according to anotherexemplary embodiment of the present invention.

FIG. 7 is a cross sectional view showing a light emitting diode chiphaving a plurality of light emitting cells according to anotherexemplary embodiment of the present invention.

FIG. 8 is a simulation graph showing a change in reflectivity of adistributed Bragg reflector according to an incident angle.

FIG. 9A and FIG. 9B each show examples of improving reflectivity forlong wavelength incident light at an incident angle of 50° and 60° byincreasing the stacking number of the distributed Bragg reflector.

FIG. 10A and FIG. 10B each are plan views showing the distributed Braggreflector after a dicing process is performed.

FIG. 11 is a graph showing the reflectivity of the distributed Braggreflector according to the presence and absence of chemical mechanicalpolishing (CMP) after the sapphire substrate lapping process by a coppersurface plate.

FIG. 12 is a graph showing the reflectivity after an aluminum reflectivemetal layer is deposited on the distributed Bragg reflector manufacturedin the similar manner as FIG. 11.

FIG. 13, FIG. 14, and FIG. 15 are graphs showing the reflectivity of thedistributed Bragg reflector according to a size of a slurry particleduring the lapping process using a tin surface plate.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention is described more fully hereinafter with referenceto the accompanying drawings, in which exemplary embodiments of thepresent invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the exemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure is thorough, and willfully convey the scope of the present invention to those skilled in theart. In the drawings, the size and relative sizes of layers and regionsmay be exaggerated for clarity. Like reference numerals in the drawingsdenote like elements.

FIG. 3 is a cross-sectional view showing a light emitting diode chip 20having the distributed Bragg reflector 45 according to an exemplaryembodiment of the present invention and FIG. 4 is a magnifiedcross-sectional view of the distributed Bragg reflector 45 of FIG. 3.

Referring to FIG. 3, a light emitting diode chip 20 includes a substrate21, a light emitting structure 30, and a distributed Bragg reflector 45.In addition, the light emitting diode chip 20 may include a buffer layer23, a transparent electrode 31, a p-electrode pad 33, an n-electrode pad35, a reflective metal layer 51, and a protective layer 53.

The substrate 21 is a transparent substrate, for example, a sapphire ora SiC substrate, but not specifically limited thereto. An upper surface,i.e., front surface of the substrate 21 may have a predeterminedpattern, such as a patterned sapphire substrate (PSS). Meanwhile, anarea of the substrate 21 determines the entire chip area. In theexemplary embodiments of the present invention, as the chip area of thelight emitting diode chip is relatively increased, the reflection effectis increased. Therefore, the area of the substrate 21 may be 90,000 μm²or more. In some embodiments, it may be 1 mm² or more.

A light emitting structure 30 is positioned on the substrate 21. Thelight emitting structure 30 includes a first conductive-typesemiconductor layer 25, a second conductive-type semiconductor layer 29,and an active layer 27 interposed between the first and secondconductive-type semiconductor layers 25 and 29. In this configuration,the first conductive-type layer 25 and the second conductive-type layer29 have a conductive type opposite to each other. The firstconductive-type may be an n-type, and the second conductive-type may bea p-type, or vice versa.

The first conductive-type semiconductor layer 25, the active layer 27,and the second conductive-type semiconductor layer 29 may be made of agallium nitride-based compound semiconductor material, that is, (Al, In,Ga)N. The constituent elements and composition of the active layer 27are determined to emit light of a required wavelength, for example,ultraviolet or blue light. The first conductive-type semiconductor layer25 and/or the second conductive-type semiconductor layer 29 may beformed in a single layer structure as shown or a multi-layer structure.In addition, the active layer 27 may be formed to be a single quantumwell structure or a multi quantum well structure. In addition, a bufferlayer 23 may be interposed between the substrate 21 and the firstconductive-type semiconductor layer 25.

The semiconductor layers 25, 27, and 29 may be formed using ametal-organic chemical vapor deposition (MOCVD) technology or amolecular beam epitaxy (MBE) technology and a region of the firstconductive-type semiconductor layer 25 may be patterned to be partiallyexposed using a photolithography and etching process.

Meanwhile, the transparent electrode layer 31 may be formed of, forexample, indium tin oxide (ITO) or Ni/Au, on the second conductive-typesemiconductor layer 29. The transparent electrode layer 31 serves tospread current due to a lower specific resistance than the secondconductive-type semiconductor layer 29. A p-electrode pad 33 is formedon the transparent electrode layer 31 and an n-electrode pad 35 isformed on the first conductive-type semiconductor layer 25. As shown,the p-electrode pad 33 may be electrically connected to the secondconductive-type semiconductor layer 29 through the transparent electrodelayer 31.

Meanwhile, the distributed Bragg reflector 45 is positioned on the lowerportion, i.e., rear surface of the substrate 21. The distributed Braggreflector 45 includes a first distributed Bragg reflector 40 and asecond distributed Bragg reflector 50.

Referring to FIG. 4, the first distributed Bragg reflector 40 is formedby repeating a plurality of pairs of first material layers 40 a andsecond material layers 40 b and the second distributed Bragg reflector50 is formed by repeating a plurality of pairs of third material layers50 a and fourth material layers 50 b. The plurality of pairs of firstmaterial layer 40 a and second material layer 40 b have relativelyhigher reflectivity for light of a red wavelength range, for example,550 nm or 630 nm, than for light of a blue wavelength range and thesecond distributed Bragg reflector 50 may have relatively higherreflectivity for light of a blue wavelength range, for example, light of460 nm than for light of a red or green wavelength range. In this case,the optical thickness of the material layers 40 a and 40 b within thefirst distributed Bragg reflector 40 is thicker than the opticalthickness of the material layers 50 a and 50 b within the seconddistributed Bragg reflector 50, or vice versa, without being limitedthereto.

The first material layer 40 a may be the same material as the thirdmaterial layer 50 a, that is, have the same refractive index (n), andthe second material layer 40 b may be the same material as the fourthmaterial layer 50 b, that is, have the same refractive index (n). Forexample, the first material layer 40 a and the third material layer 50 amay be made of TiO₂ (n equals about 2.5) and the second material layer40 b and the fourth material layer 50 b may be made of SiO₂ (n equalsabout 1.5).

Meanwhile, the optical thickness (refractive index×thickness) of thefirst material layer 40 a may substantially have the relationship of aninteger multiple with the optical thickness of the second material layer40 b, and the optical thicknesses thereof may be substantially the sameas each other. In addition, the optical thickness of the third materiallayer 50 a may substantially have the relationship of an integermultiple with the optical thickness of the fourth material layer 50 b,and the optical thicknesses thereof may be substantially the same aseach other.

In addition, the optical thickness of the first material layer 40 a maybe thicker than that of the third material layer 50 a and the opticalthickness of the second material layer 40 b may be thicker than that ofthe fourth material layer 50 b. The optical thickness of the first tofourth material layers 40 a, 40 b, 50 a, and 50 b may be controlled bycontrolling the refractive index and/or thickness of each materiallayer.

Referring back to FIG. 3, the reflective metal layer 51 of Al, Ag, orRh, or the like, may be formed on the lower portion of the distributedBragg reflector 45 and a protective layer 53 for protecting thedistributed Bragg reflector 45 may be formed thereon. The protectivelayer 53 may be made of any one metal layer of, for example, Ti, Cr, Ni,Pt, Ta, and Au or an alloy thereof. The reflective metal layer 51 or theprotective layer 53 protects the distributed Bragg reflector 45 fromexternal impact or pollution. For example, the reflective metal layer 51or the protective layer 53 prevents the distributed Bragg reflector 45from being deformed from a material such as an adhesive when the lightemitting diode chip is mounted in the light emitting diode package. Inaddition, the reflective metal layer 51 may reflect light transmittedthrough the distributed Bragg reflector 45. Therefore, the thickness ofthe distributed Bragg reflector 45 may be relatively reduced. Thedistributed Bragg reflector 45 shows relatively high reflectivity, butmay transmit visible light of a long wavelength range having a largeincident angle. Therefore, the reflective metal layer 51 may be disposedon the lower portion of the distributed Bragg reflector 45 to reflectlight transmitted through the distributed Bragg reflector 45, therebyimproving light emission efficiency.

According to the present exemplary embodiment, the distributed Braggreflector 45 including the first distributed Bragg reflector 40 havinghigh reflectivity for visible light of a relatively long wavelength andthe second distributed Bragg reflector 50 having high reflectivity forvisible light of a relatively short wavelength is provided, wherein thefirst distributed Bragg reflector 40 and the second distributed Braggreflector 50 are stacked to form the distributed Bragg reflector 45. Thedistributed Bragg reflector 45 may increase the reflectivity for lightover most of the visible range by a combination of the first distributedBragg reflector 40 and the second distributed Bragg reflector 50.

The distributed Bragg reflector according to the related art has highreflectivity for light of a specific wavelength range but has relativelylow reflectivity for light of a different wavelength range, such thatthere is a limit in improving the light emission efficiency in the lightemitting diode package emitting white light. However, according to thepresent exemplary embodiment, the distributed Bragg reflector 45 mayhave high reflectivity for light of the blue wavelength range as well ashigh reflectivity for light of the green wavelength range and light ofthe red wavelength range, thereby making it possible to improve lightemission efficiency of the light emitting diode package.

In addition, as compared to the case where the second distributed Braggreflector 50 is disposed to be closer to the substrate 21 than the firstdistributed Bragg reflector 40, the light loss in the distributed Braggreflector 45 may be further reduced in the case where the firstdistributed Bragg reflector 40 is disposed to be closer to the substratethan the second distributed Bragg reflector 50.

Although the present exemplary embodiment describes two reflectors,i.e., the first distributed Bragg reflector 40 and the seconddistributed Bragg reflector 50, more reflectors may be used. In thiscase, the reflectors having relatively higher reflectivity for a longwavelength may be positioned to be relatively closer to the lightemitting structure 30.

In addition, in the present exemplary embodiment, the thicknesses of thefirst material layers 40 a within the first distributed Bragg reflector40 may be different from each other. Further, the thicknesses of thesecond material layers 40 b may be different from each other. Inaddition, the thicknesses of the third material layers 50 a within thesecond distributed Bragg reflector 50 may be different from each other.Further, the thicknesses of the fourth material layers 50 b may bedifferent from each other.

The present exemplary embodiment describes that the material layers 40a, 40 b, 50 a, and 50 b are made of SiO₂ or TiO₂, but is not limitedthereto. Therefore, they may be made of, other materials, for example,Si₃N₄, a compound semiconductor, or the like. However, the difference inthe refractive indexes between the first material layer 40 a and thesecond material layer 40 b and the difference in the refractive indexesbetween the third material layer 50 a and the fourth material layer 50 bmay be at least 0.5.

In addition, the larger the number of pairs of the first material layers40 a and the second material layers 40 b in the first distributed Braggreflector 40 and the number of pairs of the third material layers 50 aand the fourth material layers 50 b in the second distributed Braggreflector 50, the higher the reflectivity becomes. The total number ofpairs may be 20 or more total pairs.

The surface roughness of the rear surface of the substrate 21 may becontrolled before forming the distributed Bragg reflector 45. When thesurface roughness of the rear surface of the substrate 21 is relativelylarge, it may be difficult to obtain high reflectivity over a widewavelength range by the distributed Bragg reflector 45. When theinterface between the distributed Bragg reflector 45 and the substrate21 is defective, the distributed Bragg reflector 45 may be easilydeformed. The deformation may cause a problem of reducing reflectivityof the distributed Bragg reflector 45 even if a slight thermal processis applied when the light emitting diode chip is mounted in, forexample, the light emitting diode package. The surface roughness of therear surface of the substrate 21 may be controlled to haveroot-mean-square (RMS) value of 3 nm or less. Alternatively, the surfaceroughness of the rear surface of the substrate 21 may have an RMS valueof 2 nm or less. In some embodiments, it may have an RMS value of 1 nmor less.

A method of fabricating a distributed Bragg reflector 45 and a lightemitting diode chip will now be described.

First, the surface roughness of the substrate 21 is controlled beforeforming the distributed Bragg reflector 45. For example, the rearsurface of the substrate 21 on which the light emitting structures areformed is primarily ground to remove a part of the substrate 21. In thiscase, the rear surface of the substrate 21 is scratched by the grinding,such that it is relatively very rough. Thereafter, the surface of thesubstrate 21 is lapped using slurry having small particles. In thelapping process, the depth of the groove such as the scratch in thesurface of the substrate 21, etc., is reduced, thereby reducing thesurface roughness. In this case, the surface roughness of the rearsurface of the substrate 21 may be controlled to be 3 um or less bycontrolling a particle size of diamond slurry and a surface plate usedin the lapping process. However, generally, it is difficult to controlthe surface roughness using only the lapping process using the surfaceplate and the slurry particle. Therefore, after reducing the surfaceroughness by the lapping process, the rear surface of the substrate 21may be polished by a chemical mechanical polishing (CMP) process. Thesurface roughness of the rear surface of the substrate 21 may becontrolled up to 1 nm or less by the CMP process.

Then, the material layers having different refractive indexes, such asTiO₂, SiO₂, and Si₃N₄, or the like are alternately deposited on thesurface of the substrate 21. The deposition of the material layers maybe made by various methods such as sputtering, electron beam deposition,plasma enhanced chemical vapor deposition (PECVD) method, etc. Inparticular, the ion assisted deposition may be used. The ion assisteddeposition forms the material layers having the proper thickness bymeasuring the reflectivity of the material layer deposited on thesubstrate 21, such that it is suitable to form the material layers ofthe distributed Bragg reflector.

After the distributed Bragg reflector is formed, the metal layer may beformed on the distributed Bragg reflector. Thereafter, the substrate isdiced, thereby completing the individual light emitting diode chips.

FIG. 5 is a cross-sectional view showing a distributed Bragg reflector55 according to another exemplary embodiment of the present invention.The light emitting diode chip according to the present exemplaryembodiment is substantially similar to the light emitting diode chipdescribed with reference to FIG. 3 and FIG. 4. FIG. 3 and FIG. 4 showand describe when the distributed Bragg reflector 45 has the stackedstructure of the first distributed Bragg reflector 40 and the seconddistributed Bragg reflector 50. On the other hand, in the distributedBragg reflector 55 according to the present exemplary embodiment, aplurality of pairs of first material layers 40 a and second materiallayers 40 b are mixed with a plurality of pairs of third material layers50 a and a fourth material layers 50 b. In other words, at least onepair of the third material layer 50 a and the fourth material layer 50 bis positioned between the plurality of pairs of the first material layer40 a and the second material layer 40 b. Further, at least one pair ofthe first material layer 40 a and the second material layer 40 b ispositioned between the plurality of pairs of the third material layer 50a and the fourth material layer 50 b. In this configuration, the opticalthickness of the first to fourth material layers 40 a, 40 b, 50 a, and50 b is controlled to have high reflectivity for light over the widevisible range. Therefore, the optical thickness of each material layerconfiguring the distributed Bragg reflector may be different from eachother.

FIG. 6 is a cross-sectional view showing a light emitting diode chip 20a having a plurality of light emitting cells according to anotherexemplary embodiment of the present invention.

Referring to FIG. 6, the light emitting diode chip 20 a includes aplurality of light emitting cells on the substrate 21. In addition, thelight emitting diode chip 20 a may include a distributed Bragg reflector45 and metal layers 51 and/or 53.

The substrate 21 and the distributed Bragg reflector 45 is similar tothe distributed Bragg reflector described with referenced to FIG. 3,FIG. 4 and FIG. 5 and therefore, a detailed description thereof will beomitted. However, the substrate 21 may be an insulator to electricallyisolate the plurality of light emitting cells. For example, thesubstrate 21 may be a patterned sapphire substrate.

Meanwhile, the plurality of light emitting cells 30 are positioned to bespaced apart from each other. Each of the plurality of light emittingcells 30 is the same as the light emitting structure 30 with referenceto FIG. 3 and the detailed description thereof will be omitted. Inaddition, the buffer layers 23 may be interposed between the lightemitting cells 30 and the substrate 21 and the buffer layers 23 may bealso spaced apart from each other.

The first insulating layer 37 covers the front surface of the lightemitting cells 30. A first insulating layer 37 has openings on the firstconductive-type semiconductor layers 25 and openings on the secondconductive-type semiconductor layers 29. The side walls of the lightemitting cells 30 are covered by the first insulating layer 37. Thefirst insulating layer 37 also covers the substrate 21 in the regionsbetween the light emitting cells 30. The first insulating layer 37 maybe formed of a silicon oxide (SiO₂) layer or a silicon nitride layer andmay be a layer formed in a temperature range of 200° C. to 300° C. usinga plasma chemical vapor deposition method. In this case, the firstinsulating layer 37 may be formed to have a thickness of 4500 Å to 1 μm.When the first insulating layer is formed to have a thickness less than4500 Å, the first insulating layer having a relatively small thicknessis formed due to step coverage characteristics at the bottom sides ofthe light emitting cells and an electrical short circuit between thewirings and the light emitting cells formed on the first insulatinglayer may occur. Meanwhile, as the thickness of the first insulatinglayer becomes greater, an electrical short circuit may be prevented butlight transmittance may be deteriorated to reduce the luminousefficiency. Therefore, it is preferable that the first insulating layeris formed not to exceed a thickness of 1 μm.

Meanwhile, the wirings 39 are formed on the first insulating layer 37.The wirings 39 are electrically connected to the first conductive-typesemiconductor layers 25 and the second conductive-type semiconductorlayers 29 through the openings. The transparent electrode layers 31 maybe disposed on the second conductive-type semiconductor layers 29 andthe wirings may be connected to the transparent electrode layers 31.Further, the wirings 39 electrically connect the first conductive-typesemiconductor layers 25 to the second conductive-type semiconductors 29,respectively, of the adjacent light emitting cells 30, such that aserial array of the light emitting cells 30 may be formed. A pluralityof serial arrays may be formed and are connected to each other inreverse parallel so that they may be connected to an alternating current(AC) power supply. In addition, a bridge rectifier (not shown) connectedto the serial arrays of the light emitting cells may be connected andthe light emitting cells may be driven under the AC power supply by thebridge rectifier. The bridge rectifier may be formed by connecting thelight emitting cells having the same structure as the light emittingcells 30 using the wirings 39.

On the other hand, the wirings may connect the first conductive-typesemiconductor layers 25 of the adjacent light emitting cells to eachother or connect the second conductive-type semiconductor layers 29 ofthe adjacent light emitting cells to each other. Therefore, theplurality of light emitting cells 30 connected in series and parallelmay be provided.

The wirings 39 may be made of a conductive material, for example, dopedsemiconductor material such as polycrystalline silicon or metal. Inparticular, the wirings 39 may be formed in a multi-layer structure andmay include, for example, a lower layer of Cr or Ti and an upper layerof Cr or Ti. Further, the metal layer of Au, Au/Ni, or Au/Al may beinterposed between the lower layer and the upper layer.

The second insulating layer 41 may cover the wirings 39 and the firstinsulating layer 37. The second insulating layer 41 prevents the wirings39 from being polluted from moisture, or the like and prevents thewirings 39 and the light emitting cells 30 from being damaged fromexternal impact.

The second insulating layer 41 may be formed of the same material as thefirst insulating layer 37 and the silicon oxide layer or the siliconnitride layer. The second insulating layer 41 may be a layer formed inthe temperature range of 200° C. to 300° C. by using the PECVD method,similar to the first insulating layer. In addition, when the firstinsulating layer 37 is a layer formed by using the PECVD method, thesecond insulating layer 41 may be deposited in the temperature range of−20% to +20% for the deposition temperature of the first insulatinglayer 37, or may be deposited in the same deposition temperature.

Meanwhile, the second insulating layer 41 may be relatively thin ascompared to the first insulating layer 37, and may have a thickness of500 Å or more. The second insulating layer 41 is relatively thinner thanthe first insulating layer 37, which can prevent the second insulatinglayer from peeling off from the first insulating layer. In addition,when the second insulating layer is thinner than 2500 Å, it may bedifficult to protect the wiring and the light emitting cell fromexternal impact or moisture permeation.

Meanwhile, a phosphor layer 43 may be positioned on the light emittingdiode chip 20 a. The phosphor layer 43 may be a layer in which resin isdispersed in a phosphor or a layer deposited by an electrophoresismethod. The phosphor layer 43 covers the second insulating layer 41,thereby converting the wavelength of light emitted from the lightemitting cells 30.

FIG. 7 is a cross-sectional view for explaining a light emitting diodechip 20 b having a plurality of light emitting cells according toanother exemplary embodiment of the present invention.

Referring to FIG. 7, the light emitting diode chip 20 b according to thepresent exemplary embodiment is substantially similar to theabove-mentioned light emitting diode chip 20 a, but they are differentin terms of the shape of the light emitting cells 30 and the portion ofthe first conductive-type semiconductor layer 25 to which the wirings 39are connected.

That is, the light emitting cells 30 of the light emitting diode chip 20a has the exposed upper surface of the first conductive-typesemiconductor 25 and the wiring 39 is connected to the upper surface ofthe first conductive-type semiconductor layer 25. Unlike the lightemitting diode chip 20 a, the light emitting cells 30 of the lightemitting diode chip 20 b according to the present exemplary embodimentis formed to have an inclined side surface to expose the inclined sidesurface of the first conductive-type semiconductor layer 25 and thewiring 39 is connected to the inclined side surface of the firstconductive-type semiconductor layer 25.

Therefore, according to the present exemplary embodiment, there is noneed to perform a separate process of exposing the upper surface of thefirst conductive-type semiconductor layer 25 other than the process ofseparating the light emitting cells, thereby making it possible tosimplify the process. Further, there is no need to expose the uppersurface of the first conductive-type semiconductor layer 25, therebymaking it possible to prevent the area of the active layer 27 from beingreduced. In addition, since the wiring 39 is connected along theinclined surface of the first conductive-type semiconductor layer 25,the current spreading performance of the light emitting cell 30 may beimproved and thus, the forward voltage may be reduced and thereliability of the light emitting diode chip 20 b may be improved.

EXPERIMENTAL EXAMPLE

FIG. 8 is a simulation graph showing a change in reflectivity of adistributed Bragg reflector according to an incident angle. In thiscase, the distributed Bragg reflector is made by alternately stackingSiO₂ and TiO₂ on a glass substrate by 40 layers. The thickness of eachlayer is individually controlled to have the reflectivity of 99% or moreover the entire area of 400 nm to 700 nm at an incident angle of 0°.Therefore, the thickness of the entire distributed Bragg reflector is2.908 μm. Meanwhile, in the case of the substantially used lightemitting diode chip, light incident at an incident angle of about 60° ormore is totally reflected due to the difference in refractive indexbetween the sapphire substrate (n equals about 1.78) and SiO₂ (n equalsabout 1.48) and thus, the simulation for the incident angle of 60° ormore is omitted. Meanwhile, the graph of FIG. 8 shows the entire visiblearea at the portion of 100% reflectivity (which was similarly shown inthe graph of FIG. 9).

As can be appreciated from the graph of FIG. 8, the distributed Braggreflector of 40 layers shows very high reflectivity of 99% or more withreference to the incident angle of 0° in the entire visible area.However, as the incident angle of light incident to the distributedBragg reflector is increased, it can be appreciated that thereflectivity for the visible light of a long wavelength is degraded.When the incident angle exceeds 30°, the reflectivity for light of 700nm wavelength is reduced to 99% or less.

FIG. 9A and FIG. 9B each show examples of improving reflectivity forlong wavelength incident light at an incident angle of 50° and 60° byincreasing the stacking number of the distributed Bragg reflector.

Referring to FIG. 9A and FIG. 9B, as described in FIG. 8, in the case ofthe reference distributed Bragg reflector having 40 layers (40 L) of2.908 μm total thickness, the reflectivity (40 L-50°) for the incidentangle of 50° and the reflectivity (40 L-60°) for the incident angle of60° is reduced greater than the reflectivity (40 L-0°) for the incidentangle of 0° in the visible area of a long wavelength. In addition, theportion where the reflectivity is degraded at the intermediate area ofthe visible area, for example, in the vicinity of 510 nm to 520 nmoccurs.

However, when the number of layers of the distributed Bragg reflector isincreased to 48 layers (total thickness: 3.829 μm) or 52 layers (totalthickness: 4.367 μm), it is possible to obtain substantially uniformhigh reflectivity over the wide wavelength area even though the incidentangle is large.

Therefore, an increase in the stacking number of the distributed Braggreflector makes it possible to improve the reflectivity as well asmaintain the high reflectivity for light incident at a large incidentangle. However, the increase in the stacking number of the distributedBragg reflector leads to the increase in the process time and may resultin cracks in the distributed Bragg reflector.

FIG. 10A and FIG. 10B each are plan views showing the distributed Braggreflector after a dicing process is performed. In this case, FIG. 10Ashows the case where the distributed Bragg reflector of 40 layers isstacked by an ion assisted deposition method and FIG. 10B shows the casein which the distributed Bragg reflector of 48 layers are stacked by theion assisted deposition method.

When 40 layers are stacked (FIG. 10A), cracks do not occur in thedistributed Bragg reflector and when 48 layers are stacked (FIG. 10B),cracks occur in the distributed Bragg reflector. When 52 layers arestacked (not shown), cracks may similarly occur.

The reason why cracks occurs in the distributed Bragg reflector isunclear, but is considered as being associated with the ion assisteddeposition method. That is, since the high-density layers are depositedby colliding ions, stress is accumulated in the distributed Braggreflector and thus, cracks may occur in the distributed Bragg reflectorduring the dicing of the substrate. Therefore, it may not be suitable tomass-produce the light emitting diode chip by simply increasing thestacking number.

In connection with this understanding, as described in FIG. 3, thereflective metal layer may be formed in the distributed Bragg reflector,such that the relatively high reflectivity for light having a largeincident angle may be maintained.

Table 1 shows the stacking number of the distributed Bragg reflector, akind of epoxy, and a relative light emission efficiency in the whitelight emitting diode package state according to whether the reflectivemetal layer (Al) is applied. In these experimental examples, except forthe distributed Bragg reflector, the reflective metal layer, and thetype of epoxy, other conditions, for example, the kind of the lightemitting diode chip and the kind of the package are the same. Thestacking number of layers of the distributed Bragg reflector is 40 andthe relative light emission efficiency with respect to the lightemission efficiency of the light emitting diode package (samplenumber 1) of the light emitting diode chip to which the Al reflectivemetal layer is not applied (shown by an “X”) is represented by %.

TABLE 1 Apply Reflective Relative Light Stacking Metal Kind of EmissionSample No. Number Layer (Al) Epoxy Efficiency (%) 1 40 Layer X SilverEpoxy 100 2 40 Layer X Transparent 106.8 Epoxy 3 40 Layer ◯ Silver Epoxy109.7 4 40 Layer ◯ Transparent 108.6 Epoxy 5 48 Layer X Silver Epoxy106.4 6 48 Layer X Transparent 110.9 Epoxy 7 48 Layer ◯ Silver Epoxy109.8

Comparing samples 1 and 2, and samples 5 and 6, when the Al reflectivemetal layer is not applied, it can be appreciated that the difference inthe light emission efficiency appears according to the kind of epoxyused as an adhesive. That is, a sample using a transparent epoxy showshigher light emission efficiency than in a sample using a silver epoxy.This shows that the reflectivity of the distributed Bragg reflectivityis affected by the adhesive, when there is no Al reflective metal layer.

Meanwhile, when the same kind of adhesive is used, the sample to whichthe Al reflective metal layer is applied (shown by an “O”) shows higherlight emission efficiency than other samples. For example, comparingsamples 1 and 3, samples 2 and 4, and samples 5 and 7, it can beappreciated that the light emission efficiency is improved when the Alreflective metal layer is applied.

Meanwhile, comparing sample 1 and sample 5, and sample 2 and sample 6,when the same adhesive is used and the Al reflective metal layer is notapplied, it can be appreciated that the light emission efficiency isimproved according to the increase in the stacking number. It isunderstood that the increase of the stacking number of distributed Braggreflector improves reflectivity of the distributed Bragg reflector inthe wide incident angle range, thereby resulting to improvement of thelight emission efficiency.

However, comparing sample 3 and sample 7, when the Al reflective metallayer and the silver epoxy are applied, there is no difference in thelight emission efficiency despite the increase in stacking number.Relatively high reflectivity is maintained for the visible light of thelong wavelength having a large incident angle by the Al reflective metallayer. Therefore, when the distributed Bragg reflector and thereflective metal layer are applied, it can be appreciated that the goodlight emission efficiency can be achieved at the package level whilereducing the stacking number of the distributed Bragg reflector. Inaddition, the reduction in the stacking number of the distributed Braggreflector can prevent cracks occurring in the distributed Braggreflector.

Meanwhile, when the Al reflective metal layer is applied to thedistributed Bragg reflector, it is observed that the reflectivity of thedistributed Bragg reflector is reduced at the chip level. Thisphenomenon is considered as being closely associated with the surfaceroughness of the substrate. Hereinafter, it will be described that thesurface roughness of the substrate has an effect on the reflectivity ofthe distributed Bragg reflector at the chip level.

FIG. 11 is a graph showing the reflectivity of the distributed Braggreflector according to whether or not the CMP is performed after asapphire substrate lapping process using a copper surface plate.

First, after the rear surface of the sapphire substrate is ground, thelapping process using the copper surface plate was performed by usingthe diamond slurry having a particle of 3 μm . After the lapping processwas performed using the copper surface plate, the surface roughness ofthe rear surface of the sapphire substrate showed a root-mean-square(RMS) value of about 5.12 nm at an area of 5 μm×5 μm.

Thereafter, after the rear surface of the sapphire substrate issubjected to the CMP process, the above-mentioned first distributedBragg reflector and second distributed Bragg reflector are formed bycontrolling the thickness of TiO₂ and SiO₂ to fabricate the sample(Example 1). On the other hand, the comparative example directly formedthe distributed Bragg reflector similar to Example 1 without performingthe CMP process to fabricate the sample. The CMP process was performedusing a slurry of SiO₂ at a load of 20 kg and the surface roughness ofthe sapphire substrate showed the RMS value of about 0.25 nm at an areaof 5 μm×5 μm after the CMP process.

In the case of the comparative example, the reflectivity of thedistributed Bragg reflector showed approximately 90% or more in thevisible range as shown in FIG. 10, but the reflectivity was irregularaccording to the wavelength and showed the value of 90% or less in thevicinity of 550 nm. On the other hand, in the case of example 1, most ofthe reflectivity of the distributed Bragg reflector showed a value closeto 100% over the wide wavelength range of the visible light.

FIG. 12 is a graph showing the reflectivity after an aluminum layer ofabout 500 nm is deposited on the sample fabricated in the same manner asthe example and the comparative example of FIG. 11.

In the case of comparative example, it was confirmed that thereflectivity was considerably reduced after Al was deposited. On theother hand, in the case of the example, high reflectivity was maintainedwithout reducing reflectivity even after Al was deposited.

In the comparative example, it is considered as the phenomenon that thereduction in the reflectivity is showed after Al was deposited since thedistributed Bragg reflector according to the comparative example formedon the sapphire surface having a rough surface was deformed by theinterfacial defect while the Al was deposited using the electronic beamdeposition technology. In the case of the example 1, since the surfaceroughness of the sapphire substrate is good, it is determined thatreflectivity was maintained without deforming the distributed Braggreflector while Al is deposited.

FIG. 13, FIG. 14 and FIG. 15 are graphs showing the reflectivity of thedistributed Bragg reflector according to a size of a slurry particleduring the lapping process using a tin surface plate.

In this configuration, the size of the slurry included in the diamondparticle and the diamond particle was 3 μm, 4 μm, and 6 μm,respectively. The surface roughness of the sapphire substrate showed theRMS value of about 2.40 nm, 3.35 nm, and 4.18 nm according to the sizeof the diamond particle after the lapping process was performed using atin surface plate.

The same distributed Bragg reflector as Example 1 was formed after thelapping process was performed by the tin surface plate and Al of 500 nmwas deposited as in the example of FIG. 8.

As could be appreciated from the figures, the reflectivity of thedistributed Bragg reflector was 90% or more over the wide wavelengthrange of the visible range after the lapping process was performed usingthe slurry of 3 μm and the tin surface plate. However, when the Al wasdeposited, the reflectivity was slightly reduced in the vicinity of 550nm.

In contrast, as shown in FIG. 14 and FIG. 15, the reflectivity of thedistributed Bragg reflector does not reach 90% in the vicinity of 550 nmafter the lapping process was performed using the slurry of 4 μm or 6 μmand the tin surface plate, and the reflectivity was reduced to 80% orless after Al was deposited.

It can be appreciated from the above experimental example that thesurface roughness of the sapphire substrate has an effect on thereflectivity of the distributed Bragg reflector before the distributedBragg reflector is formed. In addition, when the surface roughness ofthe sapphire substrate is controlled to have the RMS value of 3 nm orless, the reflectivity characteristics were relatively improved.Further, when the surface roughness of the sapphire substrate is 1 nm orless, it is expected that the reflectivity would not be reduced evenafter Al was deposited.

As apparent from the above description, according to the exemplaryembodiments of the present invention, it is possible to provide thedistributed Bragg reflector having high reflectivity over the widevisible range to improve light efficiency of the light emitting diodepackage implementing mixed color light, for example, white light.Further, it is also possible to reliably secure the reflectivity of thedistributed Bragg reflector by controlling the surface roughness of thesurface of the substrate on which the distributed Bragg reflector isformed.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of the present invention provided they come within the scopeof the appended claims and their equivalents.

What is claimed is:
 1. A light-emitting diode chip configured to emitlight of a first wavelength range and light of a second wavelengthrange, comprising: a substrate; a light-emitting structure disposed on afirst surface of the substrate, the light-emitting structure comprisingan active layer disposed between a first conductivity-type semiconductorlayer and a second conductivity-type semiconductor layer, and configuredto emit light of the first wavelength range; first and seconddistributed Bragg reflectors (DBRs) disposed on a second surface of thesubstrate; and a phosphor disposed on the light-emitting structure,wherein: the first DBR is disposed closer to the substrate than thesecond DBR; the first wavelength range comprises a blue wavelengthrange; light of the second wavelength range is converted by thephosphor; the first DBR comprises a higher reflectivity for light of thesecond wavelength range than for light of the first wavelength range;and the second DBR comprises a higher reflectivity for light of thefirst wavelength range than for light of the second wavelength range. 2.The light-emitting diode chip of claim 1, further comprising a phosphordisposed on the light-emitting structure, wherein the phosphor isconfigured to convert light of the second wavelength range.
 3. Thelight-emitting diode chip of claim 2, wherein the second wavelengthrange comprises a red wavelength range.
 4. The light-emitting diode chipof claim 2, wherein the second wavelength range comprises a greenwavelength range.
 5. The light-emitting diode chip of claim 1, whereinthe first DBR contacts the second surface of the substrate.
 6. Thelight-emitting diode chip of claim 1, wherein a surface roughness of thesecond surface of the substrate is 3 μm or less.
 7. The light-emittingdiode chip of claim 1, wherein the first surface of the substratecomprises a patterned surface.
 8. The light-emitting diode chip of claim1, wherein the area of the substrate is at least 90,000 μm².
 9. Thelight-emitting diode chip of claim 8, further comprising light-emittingcells disposed on the substrate.
 10. The light-emitting diode chip ofclaim 9, further comprising at least one light emitting cell array inwhich the light-emitting cells are connected in series.
 11. Thelight-emitting diode chip of claim 1, further comprising: a reflectivemetal layer, the first and second DBRs being disposed between thereflective metal layer and the substrate; and a protective layer, thereflective metal layer being disposed between the second DBR and theprotective layer.
 12. The light-emitting diode chip of claim 11,wherein: the reflective metal layer comprises Al, Ag, or Rh; and theprotective layer comprises at least one of Ti, Cr, Ni, Pt, Ta, and Au.13. The light-emitting diode chip of claim 1, wherein: the first DBRcomprises pairs of first material layers comprising a first opticalthickness and second material layers comprising a second opticalthickness; the second DBR comprises pairs of third material layerscomprising a third optical thickness and fourth material layerscomprising a fourth optical thickness; and the refractive index of thefirst material layers is different from the refractive index of thesecond material layers, and the refractive index of the third materiallayers is different from the refractive index of the fourth materiallayers.
 14. The light-emitting diode chip of claim 13, wherein the firstand second material layers comprise the same refractive index as thethird and fourth material layers, respectively.
 15. The light-emittingdiode chip of claim 13, wherein the first optical thickness is thickerthan the third optical thickness, and the second optical thickness isthicker than the fourth optical thickness.
 16. The light-emitting diodechip of claim 13, wherein the first optical thickness and the secondoptical thickness are the same, and the third optical thickness and thefourth optical thickness are the same.
 17. A method of fabricating alight-emitting diode chip configured to emit light of a first wavelengthrange and light of a second wavelength range, the method comprising:forming a light-emitting structure on a first surface of a substrate,the light-emitting structure comprising: an active layer disposedbetween a first conductivity-type semiconductor layer and a secondconductivity-type semiconductor layer, and configured to emit light ofthe first wavelength range; controlling a surface roughness of a secondsurface of a substrate; forming a phosphor layer configured to emitlight of a red wavelength range on the light-emitting structure; andforming first and second distributed Bragg reflectors (DBRs) on thesecond surface of the substrate, wherein: the first DBR is disposedcloser to the substrate than the second DBR; the first wavelength rangecomprises a blue wavelength range; the first DBR comprises a higherreflectivity for light of the second wavelength range than for light ofthe first wavelength range; and the second DBR comprises a higherreflectivity for light of the first wavelength range than for light ofthe second wavelength range.
 18. The method of claim 17, whereincontrolling the surface roughness of the second surface of the substratecomprises: removing a portion of the substrate by grinding a secondsurface of the substrate; and reducing the surface roughness of thesecond surface of the substrate by lapping the substrate.
 19. The methodof claim 18, wherein the controlling the surface roughness of the secondsurface of the substrate further comprises surface-processing the secondsurface of the substrate using a chemical after performing the lapping.20. The method of claim 17, wherein forming the first and second DBRs onthe second surface of the substrate comprises alternately disposing SiO₂and TiO₂ on the surface roughness-controlled second surface of thesubstrate, and wherein a layer of the first DBR closest to the substratecomprises TiO₂.